The U.S. has seized an oil tanker off the coast of Venezuela, sanctioned six additional ships and threatened more action amid a surge in military assets to the region.

U.S. forces intercepted and seized a sanctioned oil tanker off the coast of Venezuela, marking a serious escalation of tensions between the two countries.

The Skipper left Venezuela’s main oil port of Jose between December 4 and 5 after loading some 1.8 million barrels of Venezuela’s Merey heavy crude.